Field of the Invention
The present invention is related to power converters and more particularly to switch mode power converters.
Description of the Related Art
In general, battery-powered applications or other fixed power supply applications use power converters to generate usable voltage levels that differ from voltage levels provided to the applications. In an exemplary application, a subscriber line interface circuit (SLIC) provides a usable voltage level to a linefeed driver of a communications interface between the digital switching network of a central office and an analog subscriber line. The analog subscriber line connects to a subscriber station or telephone instrument at a location remote from the central office exchange. The analog subscriber line and subscriber equipment form a subscriber loop. The interface requirements of a SLIC result in the need to provide relatively high voltages and currents for control signaling with respect to the subscriber equipment on the subscriber loop. Voiceband communications are low voltage analog signals on the subscriber loop. Thus, the SLIC must detect and transform low voltage analog signals into digital data for transmitting communications received from the subscriber equipment to the digital network. For bi-directional communication, the SLIC must also transform digital data received from the digital network into low voltage analog signals for transmission on the subscriber loop to the subscriber equipment.
In general, the SLIC must be provided with a negative voltage supply sufficient to accommodate the most negative loop voltage while maintaining the SLIC internal circuitry in its normal region of operation. In order to ensure sufficient supply levels, a power supply providing a constant or fixed supply level sufficient to meet or exceed the requirements of all of these states may be provided. A typical SLIC uses switching circuitry (e.g., DC-DC converter) to generate appropriate supply levels from another fixed supply. The switching circuitry can be controlled to track the level needed by the SLIC and provide a variable supply level. Instead of multiple fixed power supplies to accommodate the different operational states, a single tracking supply varies its output supply level to meet the SLIC's needs.
The operational states of individual subscriber lines are inherently independent of each other and a separate SLIC and linefeed driver are provided for each subscriber line. Each tracking power supply varies its output power level in accordance with the requirements of its associated channel or device. However, such architecture may not be economical to implement, particularly with respect to a large number of channels.